1. Field of the Invention
This invention relates to the preparation of oximes from essentially water insoluble carbonyl compounds, i.e. ketones or aldehydes, and in particular to improved processes which employ a phase transfer catalyst. Hydroxyoximes prepared by the improved method are useful as metal extractants.
2. Description of Related Art
As described in U.S. Pat. No. 4,868,334, oximes are generally produced by reacting an organic carbonyl compound such as an aldehyde or ketone with hydroxylamine, usually generated from a hydroxylamine salt such as hydroxylammonium sulfate or hydroxylammonium chloride.
Current oximation procedures, particularly of long alkyl chain ketones, employ standard oximation processes with an alcohol, such as methanol as a solvent, hydroxylammonium sulfate and sodium acetate. Since sodium acetate must be anhydrous and is considerably more expensive than sodium carbonate, attempts have been made to employ sodium carbonate in the ketoximation procedure, but such attempts have not been successful.
U.S. Pat. No. 4,133,834 describes the general preparation of alpha and beta-hydroxyoximes generally useful as extractants for metals such as copper from aqueous solutions and discusses, as exemplary processes, those of U.S. Pat. Nos. 3,449,066 and 3,592,775 relative to the preparation of aliphatic, alpha-hydroxyoximes, from the corresponding acyloins and beta-hydroxyoximes from the corresponding aromatic phenones. In each of the processes the reaction is carried out under reflux conditions with an hydroxylamine salt in an alcohol medium (such as methanol) in the presence of a weak base, such as sodium acetate. Such methods typically required long reaction times for completion, particularly when the oximes included aromatic groups. U.S. Pat. No. 4,133,834 describes a process for reducing the time of reaction by employing catalytic amounts of iron, Fe.sup.+2 and Fe.sup.+3 Nawal K. Mathur and Chander K. Narang, in "Laboratory Experiments on Phase-Transfer-Catalyzed Reactions of Neutral Molecules", J. Chem. Ed., 67, p. 273, March 1990, describe the oximation of benzophenone by first preparing an aqueous solution of hydroxylammonium chloride (1 equiv/equiv of ketone) in water and neutralizing with sodium hydroxide (1 equiv). This results in high concentration of free hydroxylamine being present all at once, which in large scale operations would present an unsafe condition. To this is added an equal volume of toluene containing 1 equivalent of benzophenone and 1 equivalent (stoichiometric amount) of 2-ethylhexanoic acid at 60.degree. C. for 1.5 hour. In the reaction mixture the level of water is 53.5 moles/mole of carbonyl and the level of toluene was 4.76 g/g of ketone. The 2-ethylhexanoic acid allegedly acts as a bifunctional catalyst, i.e. a weak acid catalyst as well as a phase transfer catalyst.
The oximes, such as the hydroxy aryl ketoximes and hydroxy aryl aldoximes, which are substantially insoluble in water but soluble in water immiscible, organic solvents, such as kerosene, are useful in solvent extraction processes for recovery of metals, particularly copper, from aqueous solutions. U.S. Pat. No. 4,507,268, describes a number of such oxime reagents prepared from ketones and aldehydes, and the use thereof in liquid/liquid extraction processes.